cnn.com – Your video will begin momentarily. Washington (CNN) — The Senate blocked a measure Tuesday that would have authorized construction of the Keystone XL pipeline as Democrats chose their pro-environment base over an old friend — embattled Louisiana Sen. Mary Landrieu. The vote could just be a speedbump for the Keystone project, with Republicans ready to try again — with much better odds of success — once they take control of the Senate in January.